Methods for rapidly testing and sorting large quantities of miniature electronic components, such as chip capacitors and resistors, are well known in the art. For example, U.S. Pat. No. 4,406,373, assigned to the assignee of the present application, teaches a method in which components to be tested are arranged in banks of rows and files on a test plate. The test plate is advanced past a testing station where an electrical property of the component is tested by contacting each component with an electrical probe. The components are subsequently passed to a sorting station where each component is blown out of the test plate and into one of several receptacles depending on the determined electrical property of the component. Components to be tested may be loaded either directly into the test plate or first placed in a load plate and then transferred to the test plate.
More recently, automated rotary testers, such as the Palomar Systems, Inc. Model 18 tester (Escondido, Calif.), have been developed that can test large quantities of components at high speeds. In these testers, components to be tested and sorted are placed in slots, or holes, spaced apart on the outer circumference of a circular test plate. The test plate is rotated in a stepwise, intermittent manner towards a testing station where one or more electrical properties of the components are determined by means of electrical probes. The test plate then advances to a sorting station where the components are directed into one of several receptacles depending on the determined electrical property.
When electronic components having nearly equal length and width dimensions are tested in either linear or rotary test devices as described above, the components may be positioned in the test plate, either directly or indirectly by means of a load plate, using vibratory and/or vacuum techniques well known in the art. For example, the Palomar Systems, Inc. Model 18 rotary tester includes a rearwardly inclined circular test plate that may be loaded by simply depositing a multiplicity of components on the lower front portion of the test plate, either manually or by an automatic feed mechanism. The stepwise rotation of the test plate agitates the components sufficiently to cause them to fall into the slots on the outer circumference of the test plate.
However, these loading techniques cannot be successfully employed for electronic components of which one of the length and width dimensions is greater than the other, hereinafter referred to as elongate, terminated components. Industry practitioners define for a miniature electronic component the length as the distance between the end caps (i.e., coated ends) of the component, the thickness as the height of the internal stack of ceramic and metal layers, and the width as the remaining dimension. FIGS. 1A, 1B, and 1C show, respectively, long-side terminated, short-side terminated, and chip array components as examples of elongate, terminated components. Each of these components has an elongate rectangular body 2 and multiple electrically conductive coatings 4 that form the terminals. (The features of the individual components are identified by the suffix of the corresponding figure number.)
The difficulty associated with loading elongate, terminated devices is illustrated by FIG. 1D for short-side terminated components of the type shown in FIG. 1B. To accommodate such components, slots 6 in a test plate 8 must necessarily be wider than the smallest dimension of the components. When they enter test plate slots 6, short-side terminated components tend to stand upright, thereby resulting in a significant percentage of components standing at a 90.degree. misaligned orientation in test plate slots 6 and remaining incorrectly positioned. Moreover, a short-side terminated component such as an 0612 body, which is 0.06 inch (1.5 mm) long and 0.12 inch (3.0 mm) wide, necessitates a 0.13 inch (3.3 mm) wide test plate slot 6 that would undesirably accommodate two incorrectly loaded 0612 components standing side-by-side in one slot, as shown in FIG. 1D.
A method commonly employed for loading elongate, terminated components is the flat-load technique. As shown in FIG. 2A, short-side terminated components 10 are first placed manually in a series of shallow pockets 12 in a flat-load plate 14, with the terminals 16 of components 10 oriented towards the short sides of pockets 12. A thin slide plate 18, typically made of stainless steel, is placed between flat-load plate 14 and a slotted test plate assembly 20. Test plate assembly 20 includes a two-piece electrically nonconductive top plate 21 having slots 22 chamfered at one end and of uniform width at the other end, and a common plate 23 having a copper plated surface 24 and smaller diameter slots 26 axially aligned with corresponding slots 22 in top plate 21. The long sides of pockets 12 are generally perpendicular to the longitudinal axes of slots 22 and 26. Slide plate 18 covers pockets 12 of flat-load plate 14 to hold components 10 in place. The assembled stack of plates is inverted, as shown in FIG. 2B, and slide plate 18 is removed, thereby allowing components 10 to fall into slots 22 of test plate assembly 20 and against surface 24 of common plate 23, as shown in FIG. 2B. As shown in FIG. 2C, with flat-load plate 14 and the chamfered slot piece of top plate 21 removed, a common voltage or electrical current is then applied to copper surface 24 of common plate 23, with which bottom terminals 16b of components 10 are in contact. An electrical probe 28 is then applied against the top terminal 16t of each component 10 to measure its electrical properties.
Manual loading and flat loading are operator intensive and do not readily facilitate rapid testing of large quantities of components. There thus remains a need in the art for a method and an apparatus that permit rapid loading and positioning of large quantities of elongate, terminated electronic components for testing and processing operations.